Darwin had argued that the engine of natural selection built the most complex organs one step at a time, each step conferring an adaptive survival advantage. However, design theorists have argued that this mechanism cannot produce. They countered that any organ or structure is irreducibly complex – that they could not be constructed one step at a time. Instead, many integrated parts had to be present before an organism could derive any profit from the gradual building process.
Michael Behe demonstrated the principle of irreducible complexity by comparing a new beneficial structure with a mouse trap. In order for the mouse trap to be functional and useful, it required a minimum of five parts. Without just one of them, the trap would be of no use.
There are millions examples of irreducible complexity. Arguably, every organ or structure is irreducibly complex. A spider web is a good example of this. Von Vett and Malone write:
- Spiders are capable of producing one of the finest filaments strands known to man. These threads can be 10,000 times thinner than a strand of human hair, yet the silk is five times stronger than an equivalent weight of steel cable. Scientists have yet to learn to synthesize an equally strong artificial silk nor do they know how a spider keeps from clogging its spinnerets as the emerging silk immediately solidifies upon exposure to oxygen. (Inspired Evidence)
Von Vett and Malone marvel how the pre-spider could have evolved such an incredible substance, but also have simultaneously evolved the mechanisms and instincts necessary to use it effectively without getting caught in its own web.
In order for the spider to derive any advantage out of his silk, he would also have required the ability to make a web out of it. And these abilities and organs had to exist simultaneously! To have the silk without the instinct and tools to make the web would not have given him any advantage. Instead, the silk would have been a useless encumbrance.